Characterization of Electric Fan Noise Generation Due to Blade Geometry

Abstract

The flow surrounding the propeller of an electric fan contributes significantly to the noise emitted by low-pressure electronic fans designed to cool electronic equipment such as desktop computers. This study characterizes fan noise based on modification of geometrical features such as its hub diameter, blade length, blade thickness, blade angle of attack and number of blades. Computational Fluid Dynamics and Computational Aeroacoustics simulations were employed to analyze sound pressure level on the fan rotor. A commercially available computer cooling fan was selected as a reference fan. Two constant rotational speeds were tested, 2,400 rpm and 4,500 rpm, yielding OASPL of 31.94 dB and 48.99 dB, respectively. The sound pressure levels visualized from the reference fan were within the range of noise emission advertised by two manufacturers for the same size of fan, with number of blades and rated voltage. Velocity magnitude profiles and pressure profile distributions were also generated to visualize the flow patterns and validate aerodynamic theories citing turbulent flow in the vicinity of the rotor, characterized by a vortex field, wakes and eddies in the Trailing Edge. A reduction in hub diameter and an increase in the blade’s thickness resulted in considerable noise reduction. Consequently, an improved fan geometry was created by superimposing these design modifications yielding a 5.02 dB and 3.53 dB noise reduction for the two respective rotational speeds.